Preparation of synergistic silicon, phosphorus and nitrogen flame retardant based on cyclosiloxane and its application to cotton fabric

A novel cyclic Si/P/N flame retardant namely tetra (cyclosiloxyl-trimethoxysilylpropyl spirocyclic pentaerythritol) phosphate (SPPTMS) was successfully synthesized and applied to the finishing of cotton fabrics. The chemical structure of SPPTMS was characterized by Fourier transform infrared spectra (FT–IR) and hydrogen nuclear magnetic resonance (1H NMR). The flame retardant performance of SPPTMS treated cotton fabric was tested by limiting oxygen index (LOI), vertical flammability test, cone calorimetry test (CONE) and thermogravimetric (TG) analysis. The surface structure and element composition of cotton fabric before and after treatment was analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). When SPPTMS concentration is 350 g/L, the LOI of cotton fabric reaches 31.2%. The char residue length is 8.1 cm in the vertical flammability test. Cone calorimetry test results show that the peak heat release rate (pHRR) and total heat release (THR) of treated cotton fabric are reduced to 14.3 kW/m2 and 1.9 MJ/m2, respectively, compared with untreated cotton fabric. Thermogravimetric analysis coupled with Fourier transform infrared analysis (TG–FTIR) results show that the treated cotton fabric releases fewer combustible gases during thermal degradation than untreated cotton fabric. SEM, EDS and TG–FTIR showed that SPPTMS could promote the release of non-combustible gas and the formation of char layer to enhance the flame retardancy of cotton fabric, which indicates that SPPTMS has the flame retardant mechanism of condensed phase and gas phase.